Growth Of Bismuth Garnet Films For High Figure Of Merit Faraday Effect Devices

Abstract

Single crystal films of the bismuth substituted iron garnets have been grown by liquid phase epitaxial (LPE) procedures onto GGG or CMZGGG substrates. For switchable devices, both the optical figure of merit, defined by θ/α (0 = Faraday rotation and a= optical loss) and the magnetic properties must be controlled. We have prepared films of the type BixRE3-xFe5-yGay012 on GGG (ao = 12.383A) substrates with figures of merit greater than 1°/pm or 2°/dB at 550 nm. Single rare earths (RE) or combinations of Tm, Yb, Lu, or Y are used with 0.4 <x <0.6 and 0.8 <11. <1.2. The anisotropy field Ht, magnetization 4TrMs, and collapse field must be low to obtain switching. The optical figure of merit can be doubled by employing substrates of CMZGGG (a0 = 12.495A) to incorporate more Bi. Films of the type BixTmyGdzY3-x-y-zFe5-tGat012 were prepared by LPE growth. These films approach 4°/db at 550 nm, had also a high Curie point of 170°C, and fulfilled all magnetic parameters for switching. Switchable films are useful for structured devices such as displays, printers, modulators, pattern recognition, or cross bar switches. Many of these have been prepared with 64 to 128K independent elements. If the highest figure of merits are desired and mag-netic parameters are not critical, the amount of Bi can be increased further by using NdGG (ao = 12.51A) (or other high ao substrates such as GdScGG (a0 = 12.55A). These films are prepared in 1 - 10μm thicknesses but can be grown up to 50 - 400pm by single or multiple film methods. Thus high absolute rotations of 45 - 90° can be obtained. Such films may be used in optical isolators for fiber optics at 1.30 - 1.50μm where low insertion loss is required. The consistent growth of both low resonant linewidth (AH) and high Bi films for optical guided wave and magnetostatic wave interactions is still a challenge.